A polymer electrolyte fuel cell is composed of a cell unit, in which an anode electrode and a cathode electrode performing reactions for power generation, and a solid polymer electrolyte membrane serving as a proton conductor between the anode electrode and the cathode electrode, are sandwiched by separators.
The above electrodes are composed of an electrode substrate that accelerates gas diffusion and collects electrons and a catalyst layer where an electrochemical reaction actually takes place. Specifically, at the anode electrode a fuel gas is reacted at the catalyst layer to generate a proton and an electron, the electron is conducted to the electrode substrate and the proton is conducted through the electrode electrolyte to the solid polymer electrolyte membrane. On the other hand, at the cathode electrode, an oxidizing gas, the proton conducted from the polymer electrolyte membrane, and the electron conducted from the electrode substrate are reacted at the catalyst layer to form water.
As the solid polymer electrolyte membrane and the electrolyte in the electrode used for the above-mentioned polymer electrolyte fuel cell, a perfluoro-type electrolyte represented by Nafion (trade name, manufactured by E. I. du Pont de Nemours and Company) and various kinds of hydrocarbon electrolytes are known, and all of them require water in order to realize the proton conductivity.
Accordingly, when operation of the fuel cell is done under low humidity conditions, the electrical conductivity is decreased because the water content of the electrolyte is decreased, leading to the decrease in the output of the fuel cell. On the other hand, when the operation of the fuel cell is done under high humidity conditions, excessive water resides in the electrode because water is formed by the electrode reaction. Accordingly, if drainage of water in the electrode is insufficient, flooding takes place, leading to the decrease in the output of the fuel cell.
In order to avoid flooding under high humidity conditions, there is a case in which a water repellent agent is introduced into the electrode (for instance, refer to Patent Document 1). As such repellent agents, fluorine-containing resins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene/hexafluoropropylene copolymer (FEP), tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer (PFA), ethylene/tetrafluoroethylene copolymer (ETFE), poly(vinylidene fluoride) (PVDF) and the like are used.
By using the electrode catalyst layer containing the fluorine-containing resins, the water drainage in the electrode is improved because an improving effect of water repellency due to the fluorine-containing resins may be obtained. Therefore, the power generation performance may be improved by introducing the fluorine-containing resin when operation of the fuel cell was done under high humidity conditions, but it was not satisfactory.
In addition, when the electrode catalyst layer which contains the fluorine-containing resin is used under low humidity conditions in operation of the fuel cell, there is a problem of decrease in the output of the fuel cell and the like, because the water retention capacity in the electrode is decreased, which causes the water content in the electrolyte to decrease, leading to a decrease in the electrical conductivity.
Patent Document 1: Japanese Patent Laid-Open Publication No. H11-67225